1. Field of the Invention
The present invention relates generally to ophthalmic lens systems and associated methods, and more specifically to binocular ophthalmic lens systems and methods in which the aberrations or other optical properties of the two lenses of a lens system are different in at least one respect.
2. Description of the Related Art
Accommodation of the eye is a process in which the axial location and/or optical power of the natural lens changes in response to ciliary muscle action, thereby allowing the eye to focus on objects over a range of distances. The ability for the eye to provide accommodation generally diminishes with age, becoming particularly apparent between the ages of 40 and 50. In addition, accommodative ability may be lost altogether when the natural lens is removed an replace by an intraocular lens, for example, due to the presence of cataracts. In this case, the loss of accommodation is because the vast majority of intraocular lenses that replace the natural lens have a fixed optical power and are unable to move in response to ciliary muscle action.
Multifocal contact lenses and intraocular lenses have been used to at least partially restore a subject's ability to focus on objects at more than one distance. Typically, such lenses provide two optical powers or foci simultaneously—the lower optical power providing the ability to focus on object at distances greater than a few meters, while the higher optical power provides the ability to focus on objects that are within a meter of the subject.
One way of providing a multifocal lens is to add a multifocal diffractive pattern to a refractive lens. The diffractive pattern may be configured so that approximately half the light from an object is focused by the refractive power of the lens (e.g., for providing distant vision), while the other half is focused by the combination of the refractive power of the lens and a +1 diffraction order of the diffractive pattern (e.g., for providing near or intermediate vision). An added benefit to this approach is that the +1 diffraction order has a chromatic aberration that is opposite in sign to that produced by the refractive power of the ophthalmic lens and the cornea of the eye. By proper selection of the diffractive power, the total chromatic aberration of the ophthalmic lens/eye system can be significantly reduced, resulting in improved visual acuity for near or intermediate vision. However, one drawback to traditional multifocal diffractive lenses is that the chromatic aberration for the distance power of the lens is not affected, since there is no diffractive power in this focus.
Accordingly, there is a need to provide multifocal ophthalmic lens systems that provide chromatic aberration reduction for both distant vision and near or intermediate vision.